Nematomorpha
Phylum Nematomorpha are parasitic worms within the super-phylum Ecdysozoa because the have a chitinous exoskeleton. They are closely related to nematodes but are set apart by their unique life cycle. Nematomorps have an extremely small diameter and grow to a length far exceeding that of their host. For this reason they are commonly referred to as horse-hair worms.
Nemato morphs have a 4-stage (sometimes 5-stage) life cycle starting with the egg. The egg, in a fresh body of water, will hatch a non-parasitic larva of only about 100µmin length. The larva must then find a host which will start the third stage of the life cycle. This poses a problem however, because horse-hair worms must go from a body of water to within a terrestrial arthropod. This can be achieved in two ways. The first is to simply wait until the arthropod drinks from the infested water. The second involves a paratenic host, or transport host. The larvae seek a partenic host, such as aquatic insect larvae, which the definitive host will consume. Once inside the paratenic host, the horse-hair worm will not feed. Rather it will create a cyst inside the gut of this temporary host until it is consumed. This part is often considered an additional stage of the life cycle.
Once inside the definitive host the nematomorph will grow and develop. It will take up the majority of the arthropod's cavity when fully grown. When it has fully matured it will escape its host and return to freshwater. To do so the nematomorph alters the behavior of the host. For years it seemed that the host would actively search for water. Although, after lab studies it can be observed that the host is possessed into erratic behavior until it happens upon water, where it will jump in to commit suicide. The sexually mature horse-hair worm will escape the host and find a mate and restart the life cycle.
Nemato morphs have a 4-stage (sometimes 5-stage) life cycle starting with the egg. The egg, in a fresh body of water, will hatch a non-parasitic larva of only about 100µmin length. The larva must then find a host which will start the third stage of the life cycle. This poses a problem however, because horse-hair worms must go from a body of water to within a terrestrial arthropod. This can be achieved in two ways. The first is to simply wait until the arthropod drinks from the infested water. The second involves a paratenic host, or transport host. The larvae seek a partenic host, such as aquatic insect larvae, which the definitive host will consume. Once inside the paratenic host, the horse-hair worm will not feed. Rather it will create a cyst inside the gut of this temporary host until it is consumed. This part is often considered an additional stage of the life cycle.
Once inside the definitive host the nematomorph will grow and develop. It will take up the majority of the arthropod's cavity when fully grown. When it has fully matured it will escape its host and return to freshwater. To do so the nematomorph alters the behavior of the host. For years it seemed that the host would actively search for water. Although, after lab studies it can be observed that the host is possessed into erratic behavior until it happens upon water, where it will jump in to commit suicide. The sexually mature horse-hair worm will escape the host and find a mate and restart the life cycle.